1. Field of the Invention
The present invention relates to an orthodontic brace of the type that includes spring formed of a superelastic material for establishing movement of the teeth desired to be moved, and fastening means which are intended for fastening the spring means to force-transmitting means which are connected with the teeth for transmitting the actuation force of the spring means to the teeth desired to be moved.
2. The Prior Art
For a correction of misaligned teeth small locks are placed on the teeth, these locks are so-called brackets, in which it is possible to mount different types of wires, depending on the type of tooth movement desired to be carried out.
In the majority of all cases orthodontics is carried out by means of continuous arches along which the tooth movements are carried out. This technique, which is called the straight-wire-technique, is connected with drawbacks as friction arises between the locks and the wires, and as it is difficult to carry out a parallel translation along the arch. Furthermore, it is only possible to carry out tooth movements in the direction of the arch.
In order to overcome the drawbacks of the straight-wire-technique, a so-called segmented technique has been developed in which specially shaped braces are applied between groups of teeth, which braces supply forces and momenta resulting in the tooth movements. Using this technique the correction of the misaligned teeth may be controlled in a more precise way.
However, this requires a thorough knowledge of the relations between the geometry of the teeth, bone support, and the mechanical properties of the braces. It is especially important to have a precise knowledge of how forces and momenta are released from these braces in order to obtain a desired tooth movement. Though the arches remedy some of the drawbacks of the straight-wire-technique, they are complicated to use as great degree of manual adjusting and a large professional skill is required in order to correctly apply and use the known braces. Furthermore, the known braces will not make it possible in all situations to obtain desired relations between moment and force during tooth movement, which occurs after applying the known braces.
It is also difficult to relate the forces and momenta directly to the so-called centre of resistance for a tooth. The centre of resistance is defined as the point through which the effect from simple force will result in a translation. The centre of resistance will normally be positioned approximately in the centre of a root of a tooth, that is to say, in the jawbone approximately 1/3 from the tip of the root. As the teeth are affected via brackets which are positioned on the crowns of teeth, a simple force acting on a bracket will result in a combined translation and rotation of a tooth or a tooth segment which is affected. On the contrary, a pure translation of a tooth is obtained by applying a combined force and a moment on the brackets used. When the relation between the applied moment and the applied force vary, different tooth movements are obtained, which may be a pure translation, a combined translation and rotation, or a simple rotation around the centre of resistance.
A drawback of the known techniques is the need for optimizing the actuation on the teeth in order to obtain tooth movement relative to biomechanical properties. Thus, it it desired to keep the force actuation within limits in which an optimizing of the biomechanical system occurs, so that tooth movement takes place with a speed that is as optimal as possible. This relation should also be compared to the desire to minimize adjustments of the actuation means, as this normally requires a consultation.
Another important aspect is that a tooth movement with great actuation force will also cause much unpleasantness for the patient. Accordingly, through experience it has been found that an optimal force should be between approximately 50 cN and 250 cN. In order to obtain such a comparative, well-defined and constant force, it has been previously suggested, e.g., from U.S. Pat. No. 4,849,032, to use springs from a superelastic material, as a substantially constant force may be obtained over a comparatively long spring compression. That is to say, establishment of springs which do not follow Hookes' Law of linear elastic materials.
Though the use of the superelastic springs will highly comfort the patient and simultaneously give the possibility of less frequent consultations for checking the orthodontic brace, the use will not remedy the above-mentioned drawbacks with uncertain tooth movements.
It is the object of the present invention to remedy the above-mentioned drawbacks and to provide an orthodontic brace which also makes it possible to carry out orthodontic correction of misaligned teeth according to the two known fundamentals, that is to say, with the straight-wire-technique and the segmented technique, and which simultaneously will be very easy to use and wherein a precise and unique tooth movement is obtained. At the same time, it is the object that the orthodontic brace can be prefabricated, and that there will be no subsequent need for individual adjustment and adaption when using the orthodontic brace.